was it a real swarm, or just a lot of bees?
swarms occur every so often, usually in the spring. the hive is either moving, or splitting in 2.
if it was just a lot of bees, wtf knows. prolly you had a hive nearby that was all hot and bothered for some reason or there was a great food source near you.
never understood how people can be afraid of snakes, especially ones they know are non-venomous. for that matter, the whole being afraid of organisms, of whatever persuasion, that weigh < 3-4 times your human weight seems retarded and pussyish. i can understand disgust or dislike, but fear makes no sense.